U.S. patent number 4,558,424 [Application Number 06/422,493] was granted by the patent office on 1985-12-10 for robot control apparatus.
This patent grant is currently assigned to Kabushiki Kaisha Sankyo Seiki Seisakusho. Invention is credited to Yukio Oguchi, Kazuyoshi Yasukawa.
United States Patent |
4,558,424 |
Oguchi , et al. |
December 10, 1985 |
Robot control apparatus
Abstract
A robot control apparatus for controlling the movement of an arm
of a robot with respect to a workpiece transported upon a pallet
moving down an assembly line, wherein the position of the arm of
the robot is compensated for in accordance with the position of the
workpiece. A reference position memory stores a reference position
of one of the pallet and workpiece. A position detector detects the
position at which the pallet of workpiece is clamped along the
assembly line. A difference between the outputs from the reference
position memory and the position detector is used to correct a
value stored in a work position memory to thus provide the output
data which controls the movement of the arm of the robot.
Inventors: |
Oguchi; Yukio (Nagano,
JP), Yasukawa; Kazuyoshi (Nagano, JP) |
Assignee: |
Kabushiki Kaisha Sankyo Seiki
Seisakusho (Nagano, JP)
|
Family
ID: |
23675138 |
Appl.
No.: |
06/422,493 |
Filed: |
September 23, 1982 |
Current U.S.
Class: |
700/259; 700/114;
700/193; 700/251; 700/258; 700/192 |
Current CPC
Class: |
B25J
9/161 (20130101); G05B 19/4182 (20130101); B25J
9/0093 (20130101); B25J 9/1692 (20130101); Y02P
90/02 (20151101); G05B 2219/49134 (20130101); G05B
2219/45083 (20130101); Y02P 90/083 (20151101); G05B
2219/36503 (20130101) |
Current International
Class: |
B25J
9/00 (20060101); B25J 9/16 (20060101); G05B
19/418 (20060101); G06F 015/46 () |
Field of
Search: |
;364/513,474,170,175,176
;318/568,626 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
Other References
"Giving Robots the Power to Cope," Colleen, H., Industrial Robot
Systems ASEA, Inc. .
"Displacement-State Monitoring for the Remote Center Compliance
(RCC) Realizations and Applications," DeFazio, T. L., Charles Stark
Draper Laboratory, Inc. 1979. .
"Use of Sensory Information for Improved Robot Learning," Seltzer,
D. S., Charles Stark Draper Laboratory, Inc., 1979. .
"Exploratory Reseach in Industrial Assembly Part Mating," Nevis, J.
L. et al., Charles Stark Draper Laboratory, 1978-1980..
|
Primary Examiner: Smith; Jerry
Assistant Examiner: Lastova; John R.
Attorney, Agent or Firm: Sughrue, Mion, Zinn, Macpeak, and
Seas
Claims
We claim:
1. A robot control apparatus for moving an arm of a robot with
respect to a workpiece supported on a pallet comprising:
reference position memory means for storing a reference
position;
means for positioning said pallet with respect to a reference
surface;
horizontal and vertical position detecting means for detecting a
position of a reference marker positioned on a predetermined one of
said pallet and said workpiece, in response to an output signal
generated by said positioning means;
work position memory means for storing a plurality of data values
representing a locus of movement of an arm of said robot;
comparator means for determining a difference between an output of
said position detecting means representing said position of said
reference marker and said reference position as supplied by said
reference position memory means and for correcting said data values
upon being output from said work position memory means in
accordance with said difference; and
robot control means for positioning said arm of said robot in
accordance with the corrected data values provided by said
comparator means.
2. The robot control apparatus according to claim 1, wherein said
position detecting means is attached to an arm of said robot.
3. The robot conrol apparatus according to claim 1, wherein said
reference marker comprises a reference pin fixed to said
pallet.
4. The robot control apparatus according to claim 1, wherein said
reference marker comprises a reference pin fixed to said
workpiece.
5. The robot control apparatus of any one of claims 1 or 2-4,
wherein said position detecting means comprises optical sensing
means.
6. The robot control apparatus of any one of claims 1 or 2-4,
wherein said position detecting means comprises a television
camera.
7. The robot control apparatus of any one of claims 1 or 2-4,
wherein said position detecting means comprises magnetic sensing
means.
Description
BACKGROUND OF THE INVENTION
The present invention relates to an industrial robot. More
particularly, the invention relates to an apparatus for controlling
the movements and work positions of an industrial robot.
Industrial robots are finding a wide range of application, not only
for dangerous tasks, but also for routine operations. For example,
assembly robots are currently being used on production lines for
supplying, discharging and machining parts, operations which
require highly precise positioning. The required motions are
repeatedly effected by a robot control apparatus with a
predetermined, designated point serving as a reference
position.
Production lines in which industrial robots are used employ a
transfer device with which products (workpieces) are moved along
transfer lines or free flow lines. Pallets, for instance, may be
used for the transfer device. If such pallets are positionally
displaced from the reference positions in the production line,
robot operations may become erroneous, even if the robot performs
the designated motions with high precision. Therefore, most
production lines incorporating industrial robots have been limited
to situations in which the pallets can be positioned with a very
high accuracy. In other words, most known types of industrial robot
cannot be incorporated into existing production lines. If known
robots were, on the other hand, used in such production lines, the
type of operation done by the robots was restricted due to the low
accuracy of the transfer device.
U.S. Pat. No. Re. 30,016 discloses a method and apparatus for
operating an industrial robot in which command signals representing
the position of a machine element relative to a workpiece are
varied as a function of measured unprogrammed changes in the
relative positions of the machine element and the workpiece. A
first signal is produced which is representative of the direction
and magnitude of a change in relative position between the machine
element and the workpiece. A second signal is produced which
represents an estimate of an unprogrammed change in relative
position during a queuing delay related to a number of interrupt
signals. These two signals are used to modify the command signals
which operate the machine element to cause the machine element to
move to the correct position relative to the workpiece.
United Kingdom patent application No. 2,027,938 A describes an
industrial robot system which is an improvement over that described
in the United States Reissue Patent. In the system of the United
Kingdom Patent Application, a control memory stores data
representing a precomputed optimum path of movement of the
manipulator arm for a fixed position of a workpiece. Projected
workpiece displacements are also stored therein. During playback
operations, the movement of the workpiece is detected and an
optimum path computed from the precomputed fixed path solution and
data related to the current position of the workpiece.
Neither of those two references, however, describes how the
position of a workpiece is to be measured or precisely how the
position correction operation is performed.
It is thus an object of the present invention to provide a robot
control apparatus for enabling a robot to move stably as desired
without being affected by the accuracy with which pellets can be
positioned.
SUMMARY OF THE INVENTION
According to the present invention, the above object is achieved by
providing a robot control apparatus which detects and recognizes a
position in which a pallet or workpiece is clamped and corrects the
movement of the robot arm in accordance with the detected values so
as to enable the robot arm to effect required operations smoothly
and stably with a high degree of flexibility.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a schematic plan view of a robot, a pallet clamp and a
position detector;
FIG. 2 is a block diagram of a robot control apparatus according to
the present invention;
FIG. 3 is a graph showing a coordinate system used with the
invention;
FIG. 4 is a schematic plan view of a pallet clamp and a position
detector according to another embodiment of the invention; and
FIG. 5 is a block diagram of a robot control apparatus according to
still another embodiment of the invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
The present invention will be described with reference to the
drawings which illustrate preferred embodiments of the
invention.
As shown in FIG. 1, a pallet 1, which supports a workpiece 2 at a
fixed position on its upper surface, is fed by a transporting line,
such as a transfer line or a free flow line, to a work position at
which the pallet 1 is secured in place by a clamp 3. The clamp 3 is
actuated by a clamp cylinder 4 which is advanced from a retracted
position when the pallet 1 reaches the work position to hold the
workpiece and pallet in position by pressing the pallet 1 against a
reference surface 5. An industrial robot 6 installed adjacent to
the work position has an arm 7 reciprocably movable to effect
desired operations such as supply and discharge of parts, bolt
fastening, cutting, etc.
A robot control apparatus 10 according to the present invention, as
shown in FIG. 2, includes a reference position memory 11, a
position detector 12, a comparator 13, work position memory 14, and
a robot control unit 15. The reference position memory 11 is
implemented as a PROM (Programmable Read-Only Memory) in which is
stored a reference position P.sub.0 of the pallet 1 or the
workpiece 2. The reference position P.sub.0 is represented by
coordinates (X.sub.0, Y.sub.0) in an X-Y (Cartesian) coordinate
system, as illustrated in FIG. 3.
The position detector 12, which detects the position at which the
pallet 1 or the workpiece 2 is clamped, includes an X-position
sensor 16 and a Y-position sensor 17 which produce signals
indicative of coordinate positions in the X-Y coordinate system.
The X-position sensor 16 and Y-position sensor 17 may be
implemented with contactless optical sensors or magnetic sensors,
for example, supported on the clamp 3 for detecting the position of
a reference pin 18 on the workpiece 2 by generating signals
indicative of respective positions of the reference pin. The clamp
3 has a limit switch 19 which, for example, produces a signal
representative of a condition in which the clamp 3 is clamping the
pallet 1.
The comparator 13 is supplied with an output signal from the
reference position memory 11 and an output signal from the position
detector 12, compares these signals, and delivers an output
indicative of the result of the comparison (the difference between
the compared signals) to the robot control unit 15. The work
position memory 14, which stores data corresponding to the work
position P.sub.1 of the robot 6, is preferably a PROM, as in the
case of the reference position memory 11. The robot control unit 15
corrects the stored data in the work position memory 14 with the
output from the comparator 13 and drives the robot 6 based on the
corrected data. The robot 6 is driven by a drive device 20 such as
a pulse motor. The output from the robot control unit 15 is in the
form of a train of pulses, the number of which corresponds to the
corrected data.
Operation of the robot control apparatus thus constructed will now
be described. The pallet 1 with the workpiece 2 held in position
thereon is delivered in the direction of the arrow (FIG. 1). When
the pallet 1 reaches the work position, the clamp cylinder 4 is
actuated to move the clamp 3 forward from the retracted position
unit it clamps the pallet 1 against the reference surface 5. The
limit switch 19 detects when the clamping of the pallet 1 is
completed. When the limit switch 19 produces a clamp signal, the
X-position sensor 16 and the Y-position sensor 17 detect an actual
reference position P.sub.0 based on the position of the reference
pin 18 and generate a detection signal indicative of coordinates
(x.sub.0, y.sub.0) of the reference position P.sub.0, with the
detection signal being supplied to the comparator 13. The
comparator 13 compares the reference values, that is, the
coordinates (X.sub.0, Y.sub.0) of the reference position P.sub.0
from the reference position memory 11 with the detected values,
that is, the coordinates (x.sub.0, y.sub.0) of the actual reference
position P.sub.0 and computes differences values (.DELTA.x,
.DELTA.y) therebetween. The coordinates (X.sub.1, Y.sub.1) of the
work position P.sub.1 are corrected by these computed difference
values to provide corrected coordinates which represent an actual
work position P.sub.1.
The robot control unit 15 is supplied with the corrected coordinate
values (X+.DELTA.x, Y+.DELTA.y) and converts them into a
corresponding number of pulses which are then delivered as a drive
signal to the source of drive 20. The robot 6 is thus accurately
moved to the actual work position P.sub.1. The robot 6 returns to
the original position after it has carried out the desired
operation. The above corrective action is effected each time a
pallet 1 is transferred to the working position. Thus, in
accordance with the invention, the robot 6 detects the actual work
position for each pallet 1, performs correction based on the
detected position, and effects an actual operation based on the
corrected data, with the result that the robot always effects the
desired operation accurately.
While in the embodiment of FIG. 1 the X-position sensor 16 and the
Y-position sensor 17 are attached to the clamp 3, these sensors may
be mounted on a position detector cylinder 21 separate from the
clamp 3 for movement with the cylinder 21, as in the embodiment
FIG. 4. The X-position and Y-position sensors 16, 17 however should
perform position measurements at a fixed position which can be
determined by the stroke of the clamp cylinder 4, by the position
detector cylinder 21, or by a stop (not shown). The reference pin
18 to be detected may be fixed to the pallet 1 rather than to the
workpiece 2. With such an alternative, the workpiece 2 should be
positioned with respect to the pallet 1 with increased accuracy.
The X-position and Y-position sensors 16, 17 may directly detect a
portion of the workpiece 2 or the pallet 1 instead of the reference
pin 18. The clamp cylinder 4 and the position detector cylinder 21
can be arranged so that they operate in ganged relation.
The X-position and Y-position sensors 16, 17 according to the
embodiments of FIGS. 1 and 4 are installed so as to have a
predetermined positional relation to the clamp 3. Also, of course,
means should be provided for driving the clamp cylinder 4 and the
position detector cylinder 21.
According to the embodiment shown in FIG. 5, the position detector
12 (the X-position and Y-position sensors 16, 17) are mounted on an
arm 7 of the robot 6. When the robot 6 receives a clamp completion
signal, the arm 7 is moved closely to the pallet 1 by arm drive
sources 22. When the arm 7 is stopped, the X-position and
Y-position sensors 16, 17 on the arm 7 detect the position of the
workpiece 2 or the pallet 1. The work position is corrected on the
basis of the detected data, and thereafter an actual robot
operation is carried out. With the embodiment of FIG. 5, it is
unnecessary to install the position detector 12 on the conveyor
apparatus, and thus the robot control apparatus can easily be
incorporated into existing production lines. Since a desired robot
operation is effected after the actual reference position P.sub.0
has been detected, the overall work efficiency, however, will be
somewhat reduced due to the time required for the position
detecting operation. In the arrangement illustrated in FIG. 5, the
robot control apparatus 10 temporarily holds a position detection
signal and supplies such a signal at a specified time after the
position detection operation has been completed to start comparison
and arithmetic operations. For this purpose, a timing generator 23
is provided.
In the foregoing embodiments, the pallet 1 is described as being
pressed against the reference surface 5 in the direction of the
Y-axis. As a consequence, the pallet 1 is held against the
reference surface 5 with a considerable degree of accuracy, and no
appreciable positional variations occur in the direction of the
Y-axis. Therefore, the Y-position sensor 17 may be dispensed with.
Positional differences of the pallets in the direction of the
Y-axis can be detected with a sufficiently high accuracy by adding
detected values from the Y-position sensor 17 and detected values
corresponding to a displacement of the clamp 3 as it is advanced,
and the pallet position determined from the mean value of the sums.
The robot control apparatus 10 has been described as comparing a
reference value with a detected value and correcting the
operational position of the robot 6 in accordance with the results
of the comparison. Since such comparison and correction can be
effected by a control unit on the robot 6, the robot control
apparatus 10 of the present invention may form a part of the
control unit of the robot 6. Furthermore, the comparator 13 and the
robot control unit 15 can be implemented with a central processing
unit (CPU). Specifically, a microcomputer can be utilized as the
control unit on the robot 6 so that no additional special-purpose
device or unit is needed for the control apparatus of the
invention.
With the arrangement of the present invention, the robot detects
the position of a pallet or workpiece and corrects the work
position based on the displacement, if any, of the detected
position from a reference position. As a result, the work position
is accurately controlled at all times. The robot can easily be
incorporated into production lines having a relatively low pallet
positioning accuracy. In embodiments in which the workpiece or the
pallet is positionally detected in synchronization with the clamp
operation, the length of a movement is not made longer than what is
needed to effect the desired robot motions. In the embodiments in
which the position detector is mounted on the robot arm, existing
transfer arrangements can be utilized without modification. In a
yet further embodiment, the position detector can be implemented
with a television camera.
* * * * *